I've been riding four days at least a week. I think I have been riding too hard- makes sense my quads would be tight. All the trails in my immediate area are climb, climb, climb. When I first noticed soreness I had ridden 20 miles (8 on the trail) one late afternoon and then the next morning did a killer 13 mile all fireroad/ single track with lots of elevation gain (1800 ft). And I am one of those lazy people who never made it a habit to stretch before or after exercise. So- rest, ice, slow down, strengthen, and stretch.